Fine die cast metallic parts

ABSTRACT

A finished molded metal part is produced by an injection molding system includes a feeder in which a metal is melted and a first chamber into which a desired amount of melted metal is introduced. The molded metal parts can have extremely fine dimensions, small thicknesses, and indented or protruding surface features that are molded with such low porosity that no further milling/finishing operation is required before the part is used in its finished state.

CROSS-REFERENCE OF THE RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.09/160,330, filed on Sep. 25, 1998, titled “Method And Apparatus ForManufacturing Metallic Parts by Injection Molding From the Semi-SolidState”; application Ser. No. 09/160,976, also filed on Sep. 25, 1998,titled “Method and Apparatus for Manufacturing Metallic Parts by FineDie Casting” which issued as U.S. Pat. No. 5,983,976, on Nov. 16, 1999,and provisional application Ser. No. 06/080,078, filed Mar. 31, 1998,the disclosures of which are hereby incorporated by reference into thisapplication in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to fine die cast metallic parts, more particularlyto fine die cast metallic parts produced by a process involvinginjection of a melted metal into a mold.

2. Description of the Related Art

One conventional method used to produce molded metallic parts frommelted metal is by die casting. Die casting methods use liquid metalduring casting and, as a consequence, molded metallic parts producedfrom this method can have low densities. Molded metallic parts havinglow densities are not generally desirable because of their reducedmechanical strength, higher porosity, and larger micro shrinkage. It isthus difficult to accurately dimension conventional molded metallicparts and, once dimensioned, to maintain their shapes. Moreover, moldedmetallic parts produced from conventional die casting have difficulty inreducing the resilient stresses developed therein.

Thixotropic methods for producing molded metallic parts generallyimprove upon the die casting method by injection molding a metal fromits thixotropic (semi-solid) state rather than from its liquid state.The result is a molded metallic part which has a higher density than oneproduced from the die casting method. Thixotropic methods are disclosedin U.S. Pat. Nos. 3,902,544 and 3,936,298, both of which areincorporated by reference herein.

Methods and apparatuses for manufacturing molded metallic parts frommelted metal in its thixotropic state are also disclosed in U.S. Pat.No. 5,501,226 and Japanese patent publications 5-285626 and 5-285627,which are incorporated by reference herein. Methods of converting ametal into a thixotropic state by controlled heating and shearing in anextruder are disclosed in U.S. Pat. Nos. 5,501,226, 4,694,881 and4,694,882. The systems disclosed in these patent documents areessentially in-line systems, in which the conversion of the metal alloyinto a thixotropic state is assisted by an extruder and the pressurizingof the same for the purposes of injection molding; all these steps arecarried out within a single cylindrical housing. It is difficult toaccurately control all of the process parameters within a singlecylindrical housing, especially temperature, shot volume, pressure,time, etc., and as a result, molded metallic parts of inconsistentcharacteristics are produced.

Moreover, some of these systems require that the metal supplied to thefeeder be in pellet form. As a consequence, if a molded metallic part ofundesired characteristics is produced by its system, recycling of thedefective part is not possible unless the defective part is first recastin pellet form. Furthermore, metal parts made from metal in thethixotropic state which is injected into a mold may have an unevensurface. Such metal parts require further processing before they can bepainted.

The present inventor's co-pending application, Ser. No. 08/873,922,filed on Jun. 12, 1997, which is incorporated by reference herein,describes a different and improved method for producing molded metallicparts from melted metal in a thixotropic state wherein the conversion ofmelted metal into the thixotropic state takes place in a physicallyseparate location from the location where the metal is injected into themold and under different conditions.

An improved system for manufacturing molded metallic parts, which iscapable of accurately producing molded metallic parts of specifieddimensions within a narrow density tolerance that operates with meltedmetal in a liquid state, is desired. Further, a production process formolded metallic parts that can consistently produce molded metallicparts of desired characteristics and that can easily accommodaterecycling of defective parts is desired. Further, an improved productionprocess for molded metallic parts made of lighter metals, likemagnesium, is desired.

SUMMARY OF THE INVENTION

An object of the invention is to provide a product made throughinjection of melted metal into a mold.

Another object of the invention is to provide molded metallic parts ofaccurate dimensions within a narrow density tolerance and is producedthrough the injection molding of melted metal in a liquid state.

Still another object of the invention is to. provide metallic parts ofdesired characteristics in a consistent manner.

Still another object of the invention is to provide metallic parts madeusing an injection molding system that minimizes the amount of gastrapped in liquid metal prior to its injection into the mold.

Still another object of the invention is to provide molded metallicparts having exceptionally smooth surfaces.

Still another object of the invention is to provide molded metallicparts having reduced porosity compared to parts produced by known diecasting and thixotropic methods.

Still another object of the invention is to provide molded metallicparts that do not need to be further processed before they are paintedor otherwise coated.

Still another object of the invention is to provide molded metal partsmade by an injection molding system that accommodates recycling ofdefective molded metallic parts easily.

These and other objects are accomplished by a molded metallic partproduced by an improved injection molding method comprising the steps ofintroducing melted metal into a first chamber through a feeder port,allowing at least a portion of the melted metal to flow through saidfirst chamber toward an outlet port, drawing into a second chamber atleast a portion of the melted metal through the outlet port under asuction created in said second chamber, pushing at least a portion ofthe melted metal remaining in the first chamber into said secondchamber, and injecting the melted metal from the second chamber into amold.

The improved system comprises a feeder in which the metal is melted.Melted metal is allowed to flow from the feeder through a feeder portinto a first chamber. At least a portion of the melted metal is drawninto a second chamber, assisted by suction through an outlet portleading from the first chamber into the second chamber. A ram in thefirst chamber pushes some of the remaining melted metal from the firstchamber through the outlet port leading into the second chamber, therebyforcing out gas that has accumulated in the second chamber between themelted metal and a piston (commonly referred to as the “plunger”) thatis positioned inside the second chamber. The pressure from the meltedmetal being driven into the second chamber by the ram forces the gasbetween the melted metal and the piston to flow past the piston throughthe small space between the piston and the wall of the second chamber.The piston in the second chamber then injects the melted metal, which issubstantially gas-free, into a mold. Before the injection, the piston inthe second chamber is retracted to draw in the melted metal from thefirst chamber by creating suction and also to regulate the volume ofmelted metal that is held in the second chamber prior to injection sothat it precisely corresponds to the size of the molded part.

The above-described process and system provide a very precise control ofthe injection volume, to within ±0.5% by weight or less, because theinjection volume is determined in accordance with the position of thepiston and any gas that is present in the melted metal, which can beabout 20% by volume, is forced out by operation the ram advancing,before the melted metal is injected.

Further, a molded metallic part made by the fine die-cast methodaccording to the invention is more advantageous than molded metallicparts made by current thixotropic processes because conversion of metalinto the thixotropic state takes more time. With the fine die-castmethod according to the invention, the injection cycle time is reducedto about 30 seconds, a 50% reduction when compared to currentthixotropic processes. Consequently, the molded metallic parts can beproduced much more rapidly.

Also, the method of the present invention can be used to mold parts of aliquid material that are more preferred than parts molded from currentthixotropic processes. They generally require less post-moldingprocessing, given their more accurate molding volume and smoothsurfaces. This permits a production process that is stable over manyruns.

In addition, the molded metal parts of the present invention can bemolded to have extremely fine dimensions, having thicknesses less than 1mm for a rectangular-shaped part measuring about 21.0 cm by 29.7 cm(which is roughly the size of a DIN size A4 sheet of paper) and alsohaving more complex structures.

Because the molded metallic parts according to the present invention canbe molded to have such fine dimensions and smooth surfaces, it ispossible to mold indented and protruding surface features onto thesurface of the molded metallic parts without having to apply subsequentmachining, milling, engraving, or sanding to the surface feature toobtain an acceptably finished surface. According to prior art methods,however, molded metallic parts can not be molded with such finedimensions-and smooth surfaces. Consequently, prior art molded metallicparts must be machined, milled, engraved, sanded, or otherwise finishedafter being molded in order to obtain an acceptably finished surface.Molded metallic parts according to the present invention are superior inthat the additional time consuming and expensive milling/finishingoperation is not required.

Additional objects and advantages of the invention will be set forth inthe description which follows. The objects and advantages of theinvention may be realized and obtained by means of instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail herein with reference to thedrawings in which:

FIG. 1 is a schematic illustration of a side view of the injectionmolding system according to one embodiment of the invention;

FIG. 2A is a side view showing one embodiment of a valve on the ram whenit is in the position that prevents melted metal from flowing topositions to the right of the valve;

FIG. 2B is a side view showing one embodiment of a valve on the ram whenit is in the position that permits melted metal to flow from the rightof the valve to positions to the left of the valve;

FIG. 2C is a front view showing one embodiment of a valve when it is notfitted onto the ram;

FIG. 2D is a side view showing one embodiment of a valve when it is notfitted onto the ram;

FIG. 3 is a side view of an alternative embodiment of the feeder tank;

FIG. 4A is a side view of an embodiment of the nozzle shut-off platewhich includes a die plate that rests flush against the nozzle;

FIG. 4B is a side view of an alternative embodiment of the nozzleshutoff plate which includes a recess in the die assembly to receive thenozzle; and

FIG. 4C is a front view of an alternative embodiment of a die assemblywhich has a receiving slot to guide the nozzle shut-off plate;

FIG. 4D is a side view of the shut-off plate guide and the driveassembly for the nozzle shut-off plate.

FIG. 5A is a top view of an embodiment of a loading system used to loadmetal ingots into the apparatus of the present invention;

FIG. 5B is a side view of another embodiment of a loading system whichincludes sealing doors;

FIG. 5C is a side view of an embodiment of a loading system whichincludes a vacuum pump;

FIG. 5D is a side view of an embodiment of a loading system whichincludes inert gas screens;

FIG. 5E-H are top views of an alternative embodiment of a loading systemused to load metal ingots into the apparatus of the present invention;

FIG. 5I is a three dimensional view of an alternative embodiment of aloading system used to load metal ingots into the apparatus of thepresent invention;

FIG. 5J is a side view of an elevator used to deliver the metal ingotsto the conveyor of the loading system;

FIG. 5K is a side view of an embodiment of a feeder which utilizessubstantially vertical outlet containment rods;

FIG. 6A is a photomicrograph of a metal sample made by a prior artmethod;

FIG. 6B is a photomicrograph of a metal sample made by a method of thepresent invention;

FIG. 7A is a schematic illustration of a side view of the injectionmolding system according to an embodiment of the invention whichcontains supporting fins around the ram;

FIGS. 7B-G are cross sectional and three dimensional views of specificarrangements of the support fins.

FIGS. 8A-D are side views of an embodiment of an injection chamber whichincludes a two part piston.

FIG. 9 shows the side view of plug formation in prior art injectionnozzles.

FIG. 10 is a side view of an embodiment of an injection chamber withincludes an outlet port.

FIGS. 11A-B are side views of an alternative method of operating thepiston.

FIGS. 12A-B are side views of an embodiment of a barrel which includes atwo part ram.

FIG. 13 is a perspective view of a molded metallic part made accordingto any of the preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the discussion of the preferred embodiment which follows, a metalalloy is produced by injection molding from a magnesium (Mg) alloy ingotor pellets which are melted and processed in a liquid state. However,the invention is not limited to magnesium products and is equallyapplicable to other types of materials, metals and metal alloys.

The terms “melted metal” and “melted material” as used hereinencompasses metals, metal alloys and other materials which can beconverted to a liquid state and processed in an injection moldingsystem. A wide range of such metals is potentially useful in thisinvention, including aluminum (Al), Al alloys, zinc (Zn), Zn alloys, andthe like.

Unless otherwise indicated, the terms “a” or “an” refer to one or more.Unless otherwise indicated, the term “gas” refers to any gas (includingair) that can be present in the injection chamber at start-up or that istrapped in the injection chamber and forced out during operation of theinvention's system.

Specific temperature and temperature ranges cited in the followingdescription of the preferred embodiment are applicable to the preferredembodiment for processing Mg alloy in a liquid state, but could readilybe modified in accordance with the principles of the invention by thoseskilled in the art in order to accommodate other metals and metalalloys. For example, some Zn alloys become liquid at temperatures above450° C., and the temperatures in the injection molding system of thepresent invention can be adjusted for processing of Zn alloys.

FIG. 1 illustrates an injection molding system 10 according to a firstembodiment of the invention. The system 10 includes pre-heat tank 19where Mg alloy pieces or ingots 18 are pre-heated to approximately 250°C. A conveyor belt 20 transfers the pre-heated Mg alloy pieces or ingots18 into a holding tank 12. Other transporting means can be used. Ametering device shown as a threaded screw 21 feeds the Mg alloy piecesor ingots 18 into a feeder 23. The feeder 23 is provided with at leastone heating element 25 disposed around its outer periphery. The heatingelement 25 may be of any conventional type and operates to maintain thefeeder 23 at a temperature high enough to keep the metal alloy suppliedthrough the feeder 23 in a liquid state. For a Mg alloy ingot, thistemperature would be about 600° C. or greater. Two level detectors 22detect minimum and maximum levels of melted metal in the feeder 23. Whenthe upper level detector 22 detects that the level of melted metal hasrisen to a maximum point, it relays a signal to a microprocessor controlunit (not shown) which instructs the screw 21 to stop dispensing. Whenthe lower level detector 22 detects that the level of melted metal hasbeen depleted to a minimum point, it relays a signal to the control unit10 which activates the screw 21 so that more Mg alloy is dispensed intothe feeder 23.

Preferably, sufficient metal should be kept in the feeder 23 to supplyabout 20 times the volume needed for one injection cycle (or shot). Thisis because the amount of time required to melt the metal necessary forone injection cycle is longer than the injection cycle time, which inthe preferred embodiment is about 30 seconds.

The feeder 23 further includes a filter 24, which may be in the form ofa grate whose openings are small enough to prevent Mg alloy pieces 18from falling through while they are being melted. This is primarily aconcern when the feeder 23 is initially started. After that, alloypieces will fall into the molten bath and be melted, although largerpieces could also be introduced later on without concern. A mixer (notshown) in feeder 23 may be included for the purposes of evenlydistributing the heat from the heating element 25 to the metal suppliedto the feeder 23.

The feeder 23, pre-heat tank 19, and all elements therebetween containan atmosphere of an inert gas to minimize oxidizing of the pre-heatedand melted metal. A mixture of carbon dioxide (CO₂) and sulfur fluoride(SF₆) gas is preferred. However, other gasses, such as CO₂, SF₆,nitrogen or argon may be used alone or in any combination with eachother. The inert gas may be introduced (e.g. from a pressurized tank)into the feeder 23 through port 11 to create an inert gas atmosphereabove the bath. The inert gas also travels around the screw and into thepre-heat tank 19 to also minimize oxidizing there, as well. It istherefore preferred for the entire feeding system as described to bemaintained under an inert gas environment.

The melted metal is subsequently supplied into a temperature-controlledbarrel 30 by way of gravity through a feeder port 27 which mayoptionally be supplied with a valve serving as a stopper (not shown).Preferably, no valve is present. A ram 32 is arranged coaxially with thebarrel 30 and extends along the center axis of the barrel 30. The outerdiameter of the ram 32 is smaller than the inner diameter of the barrel30 such that melted metal flows in the space between the ram 32 and thebarrel 30. The ram 32 is also controlled by motor 33 for axial movementin both retracting and advancing directions along the barrel 30 and forrotation around its own axis if stirring of the melted metal is desiredinside barrel 30.

A valve 17 is mounted around the outer circumference of the ram 32 toseparate the barrel 30 into upper and lower chambers. The valve 17 opensand closes to selectively permit and block the flow of metal between theupper and lower chambers of the barrel 30. Suitable valves having such afunction are known per se to those skilled in the art, and any of themmay be used for purposes of the present invention. Preferably, the valve17 is frictionally mounted on an inner circumference of the barrel 30and slidably mounted on the outer circumference of the ram 32 such that,when, for example, the ram 32 retracts upwardly in the barrel 30, thevalve 17 moves relative to the ram 32 to permit flow of melted metaltherethrough, and when, for example, the ram 32 advances downwardly inthe barrel 30, the valve 17 moves relative to the ram 32 to block flowtherethrough.

FIG. 2A is a side view showing one embodiment of a valve on the ram whenit is in the position that prevents melted metal from flowing topositions upstream of (to the right of) the valve. FIG. 2B is a sideview showing one embodiment of a valve on the ram when it is in theposition that permits melted metal to flow downstream of the valve (tothe left of the valve). FIG. 2C is a front view showing one embodimentof a valve when it is not fitted onto the ram. FIG. 2D is a side viewshowing one embodiment of a valve when it is not fitted onto the ram.

In the closed position of FIG. 2A, the rear section 17 b of the valve 17abuts the body 32 b of the ram 32. The blockage of the flow in thisposition permits the ram 32 to push the metal in the lower chamber intoan injection chamber 50 through an outlet port 37 (see FIG. 1) withoutthe metal flowing back (as shown in FIG. 2A) into the upper chamber. Inthe open position of FIG. 2B, the front section 17 a of the valve 17abuts the head 32 a of the ram 32. The metal is permitted to flowthrough the valve in this position because the front section 17 a of thevalve 17 has gaps formed between toothed portions and the flow throughthe valve 17 takes place through these gaps. As a result, when the valve17 is in the open position, the metal in the upper chamber flows intoand collects in the lower chamber.

The ram 32 as shown in the Figures has a pointed tip, but any shape maybe used, including a blunt end or a rounded end. Preferably, the end ofram 32 has a shape capable of blocking outlet port 37 to prevent theflow of melted metal between barrel 30 and injection chamber 50 if ram32 is fully advanced inside barrel 30. While injection takes place, ram32 is preferably fully advanced inside barrel 30 so that outlet port 37is closed. However, the ram 32 need not be fully advanced since valve 17and the melted metal that occupies the lower chamber of barrel 30 wouldalso prevent melted metal from leaving the second chamber duringinjection. After injection, the ram 32 is retracted (but may continuerotating if rotation is being used to stir the melted metal insidebarrel 30), and a piston 45 which is housed in the injection chamber 50begins retracting (moved to the right as shown in FIG. 1) to expand thevolume of the injection chamber 50 to a desired volume according to thedimensions of the molded part being produced. The piston 45 is stoppedwhen the volume of the injection chamber 50 becomes equal to the desiredinjection volume. The piston 45 may be retracted at the same time thatram 32 is being retracted or after ram 32 has been retracted to adesired position.

After piston 45 is stopped, the ram 32 is advanced downward, and, as aresult, a portion of the metal collected in the lower chamber of barrel30 is pushed into the injection chamber 50 through the outlet port 37.The pressure of the metal entering into injection chamber 50 assists indriving out gas present in the injection chamber 50 that accumulatesbetween the melted metal and piston 45. The ram 32 preferably advancesthrough barrel 30 until its end closes off outlet port 37, and the ram32 preferably remains in this position to keep outlet port 37 sealed offuntil injection is complete and the next shot is started.

During each shot, a certain amount of gas accumulates between the meltedmetal and the piston 45 as the melted metal enters injection chamber 50.The volume of this gas can make up as much as 20% of the volume of theinjection chamber 50. Injecting such a melted metal/gas mix into a moldcan result in molded parts that have uneven surfaces, porosity (causedby gas bubbles trapped in the metal's surface), or other imperfectionsincluding those that result from an inconsistent volume of melted metalbeing injected. Removing as much gas as possible before injection isdesired. In the method of the present invention, that gas evacuation isprimarily accomplished in two ways. First, the piston 45 and injectionchamber 50 can evacuate gas like a pharmaceutical syringe that draws inliquid from a container of liquid. Specifically, as piston 45 retracts,it creates a suction to draw in melted metal from the barrel 30 into theinjection chamber 50 and it pushes gas out behind it. Secondly, theadditional portion of melted metal driven into the second chamber by ram32 forces the gas that accumulates between the melted metal and thepiston 45 to escape around the small space between the piston 45 and thewall of the second chamber (i.e., the gas is forced out to the right ofpiston 45 due to the pressure of the melted metal). Optionally, anO-ring seal or other implement may be fitted around at least a portionof piston 45 that allows the gas to pass behind piston 45 and out of thesystem but not back in.

An injection nozzle 57 is provided with a nozzle shut-off plate 15 whichis lowered to prevent the melted metal from escaping out of theinjection chamber 50 when the ram 32 pushes the metal into the injectionchamber 50. When the injection chamber 50 has been filled with the metaland substantially all gas has been forced out, the nozzle shut-off plate15 is pulled up and the nozzle 57 is moved forward (to the left inFIG. 1) to contact the opening in a die 14. In the preferred embodiment,the movement of the nozzle 57 is achieved by mounting the entireapparatus on a slide and moving the entire apparatus towards the die 14(to the left in FIG. 1).

Simultaneously, the piston 45 is pushed to the left, relative to theinjection chamber 50, to force the melted metal in the injection chamber50 through the die 14 into a mold 13. After a pre-set dwell time, thetwo halves of the die are opened and the molded metallic part isremoved, so that a new cycle can begin.

The melted metal, while housed in injection chamber 50, is substantiallysealed off from gas that would otherwise enter injection chamber 50 fromoutside the machine by virtue of nozzle shut-off plate 15, seal 41 onpiston 45, and the melted metal which continuously occupies barrel 30during operation. Although gas is present in injection chamber 50 priorto start-up, the first run of shots drives out substantially all gas ininjection chamber 50. Thus, the melted metal that is injected frominjection chamber 50 into mold 13 is substantially free of gas.Preferably, the amount of gas present in injection chamber 50 duringinjection is less than 20%, more preferably less than or equal to 1% byvolume of the second chamber.

As shown in FIG. 1, heating elements 70 f-70 j are also provided alongthe lengths of the injection chamber 50. The temperature in the feederdiffers depending on the material present in the feeder. For the AZ91 Mgalloy, heating elements 25 are preferably controlled so that thetemperature in the feeder 23 is about 640° C. near the upper surface ofthe melted Mg alloy and about 660° C. near the lower region of feeder23. Heating elements referenced and prefixed by the numeral 70 arepreferably resistance heating elements.

In the barrel 30, the temperature near heating element 70 a ispreferably maintained at around 640° C. for the AZ91 Mg alloy. Thetemperature near heating element 70 b is preferably maintained at around650° C. for the AZ91 Mg alloy. The temperature near heating element 70 eis preferably maintained at around 630° C. for the AZ91 Mg alloy. Thesetemperatures facilitate the downward flow of metal toward outlet port 37and inhibit flow in the opposite direction.

In the injection chamber 50, the temperature near heating elements 70 h,70 i, and 70 j is preferably maintained at around 620° C. for the AZ91Mg alloy. These temperatures are sufficiently high to maintain themelted metal entirely in the liquid state from the time it exits thefeeder 23 into the barrel 30 to the time the melted metal is injectedinto the mold 14 from the injection chamber 50. The temperature nearheating elements 70 g and 70 f is preferably maintained at around 570°C. for the AZ91 Mg alloy. The lower temperature behind the seal 41 helpsprevent the metal from flowing past the seal 41.

Using the preceding temperatures at these locations permits molding ofthe AZ91 Mg alloy in the liquid state. Under these conditions, one cyclelasts approximately 30 seconds. Molded metallic parts having extremelysmooth surfaces and minimal porosity can be produced, which allows themto be painted directly without any further processing. The castings alsohave extremely accurate dimensions and consistency, and can be producedwith thicknesses of less than 1 mm when the part roughly has thedimensions of a DIN size A4 sheet of paper (21.0 cm by 29.7 cm).Preferably, the range of thickness of molded parts produced according tothe invention is between 0.5 and 1 mm for parts that have roughly thedimensions of a DIN size A4 sheet of paper. With known die casting andthixotropic methods, thicknesses no less than about 1.3 mm can beobtained for parts that have roughly the dimensions of a DIN size A4sheet of paper.

FIGS. 6A shows a photomicrograph of a Mg alloy sample made by aconventional thixotropic method at a magnification of 350 times. Asnoted previously, the prior art requires injection molding of the metalfrom its thixotropic state in order to obtain sufficiently high metaldensity to improve the mechanical strength of the cast metal part.

FIG. 6B shows a photomicrograph of a Mg alloy sample made by the methodof the current invention at a magnification of 350 times. The samplearea and thickness are similar to those of the sample shown in FIG. 6A.The sample in FIG. 6B was made by fine die casting the metal from itsliquid state according to this invention. The surface of the sample isextremely smooth and has no visible voids. Such a sample can be painteddirectly without any further processing, thus reducing process cost.Furthermore, the sample made according to the present invention hasminimal porosity and high strength. Thus, it is believed that the methodof the current invention is the first method that allows the achievementof a low porosity cast metal together with a smooth surface thatrequires no further processing, because it is the first process thatuses a uniform liquid metal volume that is substantially free of trappedgas. The prior art cast metal parts made by liquid state injectionmethods suffer from high porosity and low mechanical strength due to thetrapped gas in the liquid metal. As a result of the high porosity of theprior art cast metal parts, surface features that are indented orprotruding from the surface of the metal parts must be subsequentlymachined, milled, engraved, sanded, or otherwise finished in order toobtain an acceptably finished product.

FIG. 3 shows an alternative embodiment of the invention having a feeder23′. Like the feeder 23 of FIG. 1, the feeder 23′ of FIG. 3 includesmetering screw 21′, level indicators 22′, and heating elements 25′.However, the feeder 23′ of FIG. 3 has a lower region with a bottomsurface that is at a lower position than feeder port 27′. This lowerregion catches sludge and other material that is heavier than the meltedmetal and prevents them from passing through the feeder port 27′,ensuring that pure melted metal enters barrel 30. Another opening (notshown) may be provided from this lower region for periodicallyextracting the heavier material.

FIG. 4A shows an alternative embodiment of the invention having a nozzleshut-off plate 15′ that is positioned a predetermined distance away froma die 14′. In this alternative embodiment, when the nozzle shut-offplate 15′ is pulled up, the nozzle 57 is pushed to the left to enter arelatively deep recess that extends partially into support walls 59 and60. Die 14′ is then positioned to abut support walls 59 and 60. Therecess ensures proper alignment of the nozzle 57′ with the opening thatleads into mold 13′. The nozzle shut-off plate may be maintained at atemperature that minimizes solidification of the liquid metal in thenozzle. This may be achieved by providing a heating element on or insidethe shut-off plate. However, the plate may also be left unheated.

FIG. 4B shows a side view of an alternative embodiment of the inventionhaving a nozzle shut-off plate 15′ that retracts and advances through aslot just inside the right edge of die 14′. In this alternativeembodiment, when the nozzle shut-off plate 15′ is pulled up, the nozzle57′ is pushed to the left to enter a relatively shallow recess thatextends partially into the die 14′. The shallow recess ensures properalignment of the nozzle 57′ with the opening that leads into mold 13′.Support walls 59′ and 60′ assist in aligning the nozzle.

FIG. 4C shows a front view of an alternative embodiment of the inventionhaving a nozzle shut-off plate 15″′ that retracts and advances through aslot in the face of die 14″′. In this alternative embodiment, when thenozzle shut-off plate 15″′ is pulled up, a shallow recess, shown as thelarger circle around the smaller circle that is the opening into the die14″′, is exposed. The shallow recess ensures proper alignment of thenozzle (not shown) with the opening into die 14″′. In an alternativeembodiment (not shown), the shallow recess may be placed on supportwalls 59′ and 60′ enclosing the nozzle 57, with the shut-off platemoving within that recess.

A further embodiment of the present invention shown in FIG. 4D isdirected to operation of nozzle shut-off plates 15, 15′, 15″ and 15″′shown in FIGS. 1 and 4A-C. In this embodiment, the shut-off plate 15moves up and down between the face of the die 14 and support walls 59and 60 inside the shut-off plate guide 16. Shut-off plate guide 16 couldbe a vertical void, which can be formed between the die face and thesupport walls as shown in FIG. 1 or inside the die as shown in FIGS.4A-C. The guide 16 can also comprise a void in another direction, suchas horizontal. The shut-off plate 15 is moved through the guide 16 by acylindrical motor, an oil cylinder and/or an air cylinder 46. Thecylindrical motor 46 is held upright by a cylinder guide 47.

In one embodiment, metal ingots can be loaded into the apparatus of thepresent invention instead of metal pellets or chips. There are severaladvantages of using ingots instead of metal pellets and chips. First,the ingots are cheaper than pellets or chips. Second, the pellets tendto agglomerate into clusters on the surface of the liquid metal in thefeeder. This increases the time it takes to melt the pellets, becauseonly the pellets on the bottom of the cluster are in contact with theliquid metal. The pellets on top of the cluster are only in contact withthe solid pellets below them. On the other hand, the heavier ingots sinkto the bottom of the feeder. Therefore, since the entire ingot issurrounded by the liquid metal, it melts faster than the pellets. Aloading system configured for loading ingots may also be used to loadrecycled molded metallic parts of undesired characteristics into thefeeder without recasting the defective part in pellet form. Thus,recycled parts may be used instead of ingots according to another aspectof this embodiment.

FIG. 5A shows a top view of an alternative loading system to that shownin FIG. 1 for loading metal ingots 63 into the feeder 23. Ingots maycomprise Mg, Zn, Al or alloys thereof or other metals and alloys. Theingots 63 are transported from a first conveyor belt 61 onto a secondconveyor belt 62. A push arm 64 controlled by a conventional motor 65pushes the ingots 63 into the holding chamber 66. The push arm has asize sufficient to completely cover the opening to the holding chamber.The push arm can form an air tight seal with the opening into theholding chamber, if desired. The ingots 63 inside the holding chamber 66end up on a downward sloping part (e.g. inclined surface) 67, where amotor controlled piston 68 pushes the ingots 63 into the feeder 23. Theholding chamber is preferably maintained under an inert gas ambient,supplied from a gas port. The gas may be argon, nitrogen or a sulfurhexafluoride and carbon dioxide mix. The gas pressure in the holdingchamber 66 should preferably be maintained at a pressure above oneatmosphere to prevent outside air, which contains oxygen, from reachingthe feeder 23. The gas pressure and/or the position of the ingots may bemonitored by one or more sensors. The controlled atmosphere in theholding chamber 66 allows a decreased amount of air in the feeder andthus decreases a chance of explosion.

FIG. 5B shows a side view of another alternative loading system to thatshown in FIGS. 1 and 5A for loading metal ingots 63 into the feeder 23.The ingots 63 are transported on a conveyor 81 to a holding chamber 86,which may have a downward sloping shape. Access to the holding chamberis controlled by a first door 82. Egress from the holding chamber iscontrolled by a second door 84. The chamber may be heated by heaters 85to 100-200° C. to evaporate moisture on the surface of the ingots. Theholding chamber 86 operates as follows. First, door 82 is opened asingot 63 approaches it. Door 82 can preferably be opened by moving up,down or sideways through the walls of chamber 86. The ingot 63 entersthe chamber 86 and the first door 82 is closed. After the first door 82is closed, the second door 84 is opened and the ingot 63 moves out ofchamber 86. The conveyor 81 can move continuously through chamber 86with doors 82 and 84 opened and closed while the conveyor is moving.Alternatively, the conveyor 81 moves intermittently. It stops when aningot approaches door 82 and when the ingot is inside the chamber 86.This allows doors to be sealed hermetically. The conveyor 81 may alsoend at the sloping part of chamber 86, such that the ingots slide downunder the force of gravity.

In another alternative embodiment (not shown), the loading system shownin FIG. 5A can be used with door 82 of FIG. 5B positioned betweenconveyor 62 and chamber 66 and with door 84 of FIG. 5B positionedbetween chamber area 67 and the melt tank (e.g. melt feeder) 23. Door 82opens synchronously with the movement of the push arm 64, while door 84opens synchronously with the movement of piston 68.

The holding chamber 86 in FIG. 5B is connected to the melt tank 23″.Melt tank 23″, contains a single metal level detector 22″.Alternatively, two level detectors 22, shown in FIG. 1 can be used. Tank23″ also contains gas port 11″. An inert gas, such as at least one gasselected from a group comprising nitrogen, argon, SF₆ and CO₂, isintroduced (e.g. under pressure from a pressurized tank) into meltchamber 23″. The gas pressure of the pumped gas is preferably above oneatmosphere to keep air from entering the melt tank 23″ through holdingchamber 86 (the pumped gas flows out through chamber 86, thus preventingair from flowing into chamber 86).

The melt chamber shown in FIG. 5B also contains heaters 25″, a filter orscreen 24″ and a feeder port 27″ located above the bottom of the tank,similar to feeder tank 23′ shown in FIG. 3. The filter may be formedinside port 27″ or above port 27″, as shown in FIG. 1.

Alternatively, a vacuum pump, 87 shown in FIG. 5C can be attached inchamber 86, between doors 82 and 84. As the ingot 63 enters chamber 86,both doors 82, 84 are closed and the vacuum pump creates a near vacuumin chamber 86. Door 84 is then opened to release ingot 63 into melt tank23″ without allowing any air to enter melt tank 23″ because chamber 86was at vacuum when door 84 is opened.

As shown in FIG. 5D an inert gas screen 90 can be made to flow frominert gas source(s) 88 across the back of door 82 and/or 84 and outthrough optional suction pipes or vents 89. The inert gas screen 90keeps air from entering chamber 86 and tank 23″. The inert gas cancomprise at least on gas selected from a group comprising argon,nitrogen, CO₂ and SF₆. The gas screen of FIG. 5D can be used incombination with vacuum pump of FIG. 5C to obtain the least airpenetration into melt tank 23″. The air control measures, such as melttank gas port 11″, doors 82, 84, vacuum pump 87 and inert gas screen(s)90 are all used to prevent the introduction of air into the melt tankand/or the holding chamber to reduce the possibility of explosion.

FIGS. 5E and 5F show an alternative loading system to that shown inFIGS. 5A. The holding chamber 66′ utilizes a movable aperture plate 72.FIG. 5E shows a top view of the loading system where the access to thefeeder 23 is closed. The movable aperture plate 72 contains an aperture73 which is larger than an ingot. When no more ingots should be added tothe feeder 23, the plate 72 is moved to one side by a movable arm 74such that the plate covers the entrance to the feeder. As shown in FIG.5F, when additional ingots should be added into the feeder 23, the plate72 is moved to the other side, such that the aperture 73 corresponds tothe opening to the feeder 23. This way, the ingots coming off theconveyor 61′ pass through aperture 73 into the feeder 23. In theembodiment shown in FIGS. 5E and 5F the aperture plate 72 is utilizedinstead of a push arm 64 and piston 68 shown in FIG. 5B. However, theaperture cover plate 72 can be utilized in addition to the push arm 64and piston 68. In this case, the plate 72 is blocks access to ingotssliding down sloped surface 67.

FIGS. 5G and 5H show an alternative loading system to that shown inFIGS. 5E and 5F. In this embodiment, the holding chamber 66″ utilizes amovable cover plate 75 instead of a movable aperture plate 72. The coverplate 75 has a roughly circular shape which is sufficient to cover theopening to the feeder 23. FIG. 5G shows a top view of the loading systemwhere the access to the feeder 23 is closed. A movable arm 74′ moves thecover plate 75 over the opening to the feeder 23 to block access ofingots coming off conveyor 61″. As shown in FIG. 5H, when additionalingots should be added into the feeder 23, the cover plate 75 is movedto the other side or raised up (out of the plane of the drawing), toexpose the opening to the feeder 23. The ingots coming off the conveyor61″ can drop directly into the feeder 23. In the embodiment shown inFIGS. 5G and 5H the cover plate 75 is utilized instead of a push arm 64and piston 68 shown in FIG. 5A. However, the cover plate 75 can beutilized in addition to the push arm 64 and piston 68.

FIG. 5I shows an alternative loading system to that shown in FIG. 5A.The opening 78 to the feeder 23 is covered by a movable transfer chamber76, such as a cylinder. Cylinder 76 has an aperture 77. Aperture 77 isat the same level as the conveyor 81′, as shown in FIG. 5J. When ever itis desired to add more ingots 63 to the feeder 23, a movable arm 74″moves the cylinder into a position where the aperture 77 lines up withthe end of the conveyor 81′ to allow the ingots to fall from conveyor81′ through aperture 77 into cylinder 76 and down into the feeder 23through opening 78. To close access to the feeder 23, movable arm 74″moves the cylinder 76 in any direction (e.g. up, to the left or to theright) such that the end of the conveyor is no longer aligned with theaperture 77. While transfer chamber 76 has been described as a cylinder,it may have any other shapes, such as a cube, etc. The transfer chambermay also be used with a push arm 64 and piston 68 shown in FIG. 5A. Inthis case, the ingots 63 would slide down the sloping surface 67 intothe transfer chamber instead of dropping directly into the feeder 23.The transfer chamber 76 may also be used with the holding chamber 86FIG. 5B. This is shown in FIG. 5J.

FIG. 5J shows elevator 100 which delivers the ingots to the conveyor 81′in the holding chamber 86′. As shown in FIG. 5B, the holding chamber 86may have one or two doors (82,84). In FIG. 5J, only one door 82′ isshown for clarity. The ingots are moved up toward the holding chamber86′ on elevator platforms 101. Each platform comprises a platform base102 and a movable platform top 103 connected by at least one connector104. As each platform reaches the top of the conveyor 81′, a liftingmember 105 moves up pole 106 and pushes up on the back end of theplatform top 103. The back end of the platform top 103 is lifted aboveplatform base 102 by the lifting member 105, which causes the ingot(s)63 to slide off the platform top onto the conveyor 81′. The ingots 63pass from the conveyor 81′ into the feeder. The ingots 63 may optionallypass through the transfer chamber 76 shown in FIGS. 51 and 5J. After theingot(s) are removed from the platform top, the lifting member movesdown the pole 106, placing the platform top 103 onto the platform base102. The lifting member 105 then disengages the first platform 101, thenext platform 101 is moved up and the process is repeated.

Connector 104 may be a bolt which rotably connects platform top 103 andbase 102. Preferably, the platform top is rotated up about 20 degrees bythe lifting member 105. Alternatively, the entire platform 101, and notjust the platform top may be lifted by the lifting member. The elevator100 may also be used with the holding chamber 66 shown in FIG. 5A andingots may slide into the feeder 23 down sloped surface 67. Preferably,the movement of the lifting member 105 is synchronized with the openingof the doors. For example, as the lifting member 105 moves up on thepole 106, the door 82′ is simultaneously opened to allow the ingot 63 topass into the holding chamber 86′. Furthermore, the cover plates 72 or75 shown in FIGS. 5E-H or the transfer chamber 76 shown in FIG. 5I mayalso be synchronized with the door 82′. Thus, after the door 82′ isclosed, the cover plates or the transfer chamber may be moved to openaccess to the feeder 23. If back door 84 (shown in FIG. 5B) is alsopresent, it should be opened after the front door 82′ is closed.Elevator 100 may also be used with conveyor 61 and holding chamber 66shown in FIG. 5A.

FIG. 5K shows another embodiment of a feeder 23 utilizing substantiallyvertical outlet containment rods. In FIG. 1 (as well as FIG. 5B) feederport 27 was protected by a filter 24 is a shape of a grate. A grate isrequired to prevent unmelted metal pieces from exiting feeder 23 intothe barrel 30 through feeder port 27. However, metal ingots 63 sink tothe bottom of the feeder port and lie flat on the grate. Thispositioning is not desirable because the ingots may substantially blockliquid metal flow through feeder port 27″′ into the barrel 30. Toprevent ingots from blocking the grate, outlet containment rods 76should be utilized above the feeder port 27″′ as shown in FIG. 5K. Therods may be of any shape as long as they prevent the sinking ingots 63from laying flat across the feeder port 27″′ and blocking it. Forexample, as shown in FIG. 5K, the rods in the middle of the feeder portmay rise above the rods near the circumference of the feeder port toforce the ingots 63 to rest on their side toward the edge of the feeder23″′ while melting. Feed tank 23″′ may also have a lower region with abottom surface that is at a lower position than the feeder port 27″′, asshown in FIG. 3. The sinking ingots which come in contact with rods 76will be deflected sideways into the lower region. The ingots will meltin the lower region without blocking the feeder port 27″′.

FIG. 7A shows a side view of an alternative embodiment of the inventionhaving supporting ribs or fins 34 arranged on ram 32. FIG. 7A is not toscale and the barrel 30 thickness has been exaggerated for clarity. Theheaters 70 are present but have been omitted from FIG. 7 for clarity.The fins 34 are preferably attached to the ram 32 and can slide on theinner circumference of the barrel 30, both coaxially with the length ofthe barrel and/or in a circular motion about the barrel axis 38. Themovement produces a rotation of the fins 34 around the innercircumference of the barrel 30. Alternatively, the fins 34 may beattached to the inner circumference of the barrel 30 in such a manner asto allow the bare ram 32 to slide by. The fins 34 can be made of thesame material as the ram 32 or form a different material that canwithstand the required process temperatures. The purpose of the fins istwo fold. The first purpose is to prevent the ram 32 from tilting andwobbling away from the barrel axis 38. Since the ram 32 is fairly long,without the fins 34 it has a tendency to tilt. The unsupported frontpart of the ram comes closer to the bottom part of the interior barrelsurface than to the top interior barrel surface under the weight ofgravity. Fins 34 prevent ram from tilting and wobbling by making contactwith the inner surface of the barrel 30, thus keeping the ram 32centered and aligned with the axis of the barrel. The second purpose isto enhance the uniform temperature distribution of the melted metal.

As shown in FIG. 7A, there are no fins in area 32 c of the ram thatmoves inside valve 17 so as not to strike the valve. The cross sectionalview across section A-A′ in FIG. 7A is shown in FIG. 7B. As can be seen,the fins 34 do not extend around the entire circumference of the ram 32to allow the metal to flow through the barrel. The fins 34 can bearranged in a number of different formations around ram 32. For example,as shown in FIG. 7C, two fins can be arranged on opposite sides of therod at periodic intervals 36. Each interval can be of the same ordifferent length. For example, the fins can be spaced closed to eachother on one end of the ram than on another end of the ram, or the finscan be spaced closer together in one or more sections nearer to themiddle of the ram than one or both ends of the ram. Alternatively, asshown in FIG. 7D, more than two fins (e.g. three) can be arranged aroundthe ram at spaced intervals 39. Again, the intervals along the ram 36,and intervals around the circumference of the ram 39 can be of the sameor different length. Furthermore, the fins 34 can be tilted at one ormore angles other than 90 degrees with respect to the axis of thebarrel, as shown in FIG. 7E. Otherwise, some fins 34 may be tilted at 90degrees while other fins at an angle other than 90 degrees. As notedabove, there can be more than two tilted fins spaced along the rod atequal or unequal intervals. Still further, the width and/or thickness ofthe fins along the ram and/or around the ram circumference the maydiffer, as shown in FIG. 7F. The fins may also be staggered about thelength of the ram, as shown in FIG. 7G. In general any combination ofone of more of the above alternative arrangements are possible, even ifthe fins 34 are mounted on the inside of the barrel 30 rather than onthe 30 ram 32. The ram 32 with fins 34 may be also be used with theembodiments shown in FIGS. 3-5.

FIGS. 8A-D show side views of another embodiment of the injectionchamber 50′. In this embodiment, the piston 45′ is composed of twoparts: an inner part 46 and an outer part 47. The outer part issubstantially a hollow cylinder and the inner part is substantially acylinder which slidably fits inside the outer part. The two parts haveseparate drive mechanisms. FIG. 8A shows the situation when the ram 32is retracted back in the barrel 30 to allow metal to flow into injectionchamber 50′. The inner part 46 of the piston is fully extended to blockthe exit 58 from the injection nozzle 57″′ to prevent metal flow intothe die 14″″. The outer part 47 of the piston is retracted to expand thevolume of the injection chamber 50′ to a desired volume. Likewise, theram 32 is retracted in the barrel 30. In this configuration, metal flowsinto injection chamber 50′ from barrel 30′ but does not prematurely flowinto the die through injection nozzle aperture 58 because it is blockedby inner piston part 46. The heating elements 70 are present but areomitted from the Figure for clarity.

FIG. 8B shows the next step in the operation of the injection chamber50′. Here, ram 32 is fully advanced inside the barrel 30 to advance theremaining metal from barrel 30 to injection chamber 50′. The innerpiston part 46 is still fully advanced to block the injection nozzleaperture 58. The outer piston part 47 is still retracted to allow metalto flow from barrel 30 into injection chamber 50′. This configurationalso prevents premature flow of the metal into the die.

FIG. 8C shows the next step in the operation of the injection chamber50′. The inner piston part 46 has been retracted into the outer pistonpart 47. The injection nozzle is now open. However, no extra metal flowsfrom barrel 30 into injection chamber 50′ because barrel opening isblocked by the advanced ram 32.

FIG. 8D shows the last step in the operation of the injection chamber50′. Both the inner and outer parts 46,47 of the piston 45′ are pushedto the left to force the melted metal in the injection chamber 50′ intothe die 14″″ through the injection nozzle 57″′. As described above, theinjection nozzle 57″′ may be moved forward to contact the opening in thedie prior to moving the piston 45′ to the left.

After the step shown in FIG. 8D, the ram 32 and the outer piston part 47are retracted, while the inner piston part 46 is positioned to block theinjection nozzle aperture 58, as shown in FIG. 8A, and the process isrepeated as necessary.

Alternatively, the inner piston part 46 may be retracted partially intothe outer piston part 47, (shown as dashed lines in FIG. 8C) to allowmetal into the die opening, instead of being retracted all the way in asshown in FIG. 8C. Furthermore, the inner piston part 46 may move intothe injection nozzle 57″′ and further to the left (shown as dashed linesin FIG. 8D) than the outer piston part 47 instead of moving as far leftas the outer piston part 47, as shown by the solid line in FIG. 8D.Thus, the nozzle shut-off plate may be replaced by the inner piston part46, since both perform the same function. Thus, the apparatus of FIGS.8A-D is an improvement on the apparatus of FIG. 1 because it requiresonly one motor to move the two part piston instead of two motorsrequired in FIG. 1 (one to operate the piston and the other to operatethe shut-off plate).

Furthermore, the apparatus shown in FIGS. 8A-D prevents metalaccumulation in the nozzle aperture and allows the inner piston part 46to force the melted metal in the injection nozzle 57″′ into the dieopening. Without the two part piston, the melted metal may accumulate inthe prior art injection nozzle even after the injection motion by thepiston, and solidify as a plug 91, as shown in FIG. 9. The plug 91 formsin the exit aperture 92 of the injection nozzle 90 because the tip 93 ofthe nozzle comes in contact with the cooler walls of the die (or diesupport walls) 94. Therefore, the nozzle tip is at a lower temperaturethan the rest of the injection chamber. Such plugs are undesirablebecause they block egress from the injection nozzle, thus decreasing theamount of metal injected into the mold or rendering the apparatusinoperative.

However, the inner portion of the piston 46 in FIGS. 8A-D blocks theinjection nozzle aperture from the inside of the nozzle prior to pistoninjection movement, thus preventing any metal from accumulating in theaperture. In addition, the inner piston portion may be designed to pushout any residual metal that may accumulate in the aperture by includinga tapered tip 49 of the inner piston portion 46 that extends into theaperture, as shown in FIG. 8A.

FIG. 10 shows another embodiment of the present invention. In thisembodiment, an extra gas outlet port 110 is added. The extra gas outletport allows the gas 111 that is trapped between the melted metal 115 andthe piston 45 to escape the injection chamber. The use of outlet port110 in addition to the opening around the piston allows more gas toescape the injection chamber. Alternatively, the outlet port 110 cancomprise the only means for the trapped gasses to escape. The outletport 110 is preferably positioned between the inlet to the injectionchamber and the position of the retracted piston. The outlet port cancomprise any structure which would allow the gasses trapped in theinjection chamber to escape, without letting in the air from outside ofthe apparatus into the injection chamber and without letting the meltedmetal escape through it during injection into the mold. For example, theoutlet port 110 can contain a semi-permeable material, such as porousceramic 112. The porous material allows gas, but not melted material topass through it. The outlet port can be connected to an outlet pipe 113,which contains a one way valve 114 which allows gasses to escape, butwhich prevents outside air from entering the injection chamber.

FIGS. 11A and 11B show an alternative method of operating the piston.Prior to injecting the melted metal 115 into the mold 14, the piston ispartially advanced forward, while the nozzle shut-off plate 15 blocksmetal flow into the mold. The forward movement of the piston forces thetrapped gasses out of the injection chamber. The gasses exit through thespace between the piston and the injection chamber wall and through theoutlet port 110, if present. However, the forward movement of the pistondoes not result in the injection of the melted metal into the moldbecause the nozzle shut-off plate blocks the nozzle. Once the trappedgasses are squeezed out of the injection chamber, the shut-off plate islifted and the piston is advanced forward to inject the metal into themold, as shown in FIG. 11B.

If the two part piston shown in FIGS. 8A-D is used, then a similar gassqueeze out method can be used. With the inner portion of the two partpiston blocking the injection nozzle, the outer portion is partiallyadvanced forward to squeeze the trapped gasses out of the injectionchamber. Then, as the inner portion of the piston is retracted, theinjection nozzle is opened and the piston is advanced forward to injectthe metal into the mold.

FIG. 12A shows another embodiment of the barrel according to the presentinvention. In this embodiment, the ram is composed of two parts, aninner portion 32 d and an outer portion 32 e. The outer portion 32 e isslidably mounted on the first portion 32 d and can be advanced andretracted along the axis of the barrel 30. The inner portion 32 d isroughly circular in cross section, whole the outer portion 32 e has adoughnut shape cross section, with an inner diameter slightly largerthan the diameter of the inner portion 32 d. The two part ram operateson a principle similar to the two part piston shown in FIGS. 8A-D. Aftereach injection cycle, the inner ram portion 32 d is partially retracted,while the outer ram portion 32 e is fully retracted. As the melted metalflows from the feeder 23 through the barrel 30 and into the injectionchamber 50, the inner portion of the ram 32 d is extended down thelength of the barrel and rotates about its axis to keep the temperatureof the melted metal uniform. The outer portion 32 e is then advancedforward to push the melted metal in the barrel into the injectionchamber. Prior to the injection of the metal from the injection chamberto the mold, access to the barrel through the outlet port 37 must beclosed. This can be accomplished by blocking the outlet port 37 with theend of the inner portion of the ram 32 b or by blocking the outlet port37 with both portions of the ram. The shape of the outlet port 37 cancorrespond to the tip of the composite two part ram such that when bothportions of the ram are fully advanced, they are capable of blocking theoutlet port 37, as shown in FIG. 12B. When the outer portion 32 e isfully advanced, it substantially blocks the inlet to the barrel 30 fromthe melt feeder 23, such that substantially no melted metal enter thebarrel 30 when the outer ram portion is fully advanced.

It is important to note that all embodiments shown in FIGS. 1-12 may beused together or separately or in any combination or permutation withoutdeparting from the scope of the current invention. In other words, anyone or more improvements shown in FIGS. 2-8 may be added to the basicapparatus shown in FIG. 1 without departing from the scope of thecurrent invention.

FIG. 13 illustrates an example of a molded metallic part 200 that can bemolded according to the present invention. Molded metallic part 200 hasa surface 201 and indented surface features 202. The indentation depthof the surface features 202 is relatively small and is as molded. Whilethe surface features 202 are illustrated as words and symbols, any othertype of intentional protrusion or indentation in the surface of a moldedpart would also be considered a surface feature.

The present invention provides an advantage over the prior art in thatthe molded metallic parts 200 produced according to the presentinvention can have indented or protruding surface features 202 that aremolded with such low porosity, high smoothness and of fine dimensionsthat no substantial further machining, milling, engraving, and/orsanding is required before the molded metal part is used in its finishedstate. In other words, the surface features are of sufficient definitionand quality that no substantial further processing would be required.The surface feature could be indented or protruding above the surface ofthe molded metal part. Also, the surface feature could be continuous,such as a word. Consequently, the as molded surfaces 201 and surfacefeatures 202 of the molded metallic parts 200 according to the presentinvention may be incorporated into a product as is, or coated with apaint, varnish, glaze, etc.

While particular embodiments according to the invention have beenillustrated and described above, it will be clear that the invention cantake a variety of forms and embodiments within the scope of the appendedclaims.

1-5. (canceled)
 6. A method of making a molded metal part comprising thesteps of: introducing the melted material into a first chamber; allowingat least a portion of the melted material to pass through said firstchamber into a second chamber; pushing at least a portion of the meltedmaterial remaining in the first chamber into said second chamber;injecting the melted material from the second chamber into the mold; andforming in the mold the molded metal part, wherein the as-molded surfaceis sufficiently smooth so that the surface may be painted directlywithout further processing.
 7. The method of claim 6, wherein the moldedmetal part has a thickness less than 1 mm.
 8. The method of claim 6,wherein the thickness is in the range of approximately 0.5 mm toapproximately 1.0 mm.
 9. The method of claim 6, wherein the molded metalpart has dimensions of approximately 21.0 cm by approximately 29.7 cm.10. The method of claim 6, wherein said allowing step comprises creatinga suction in the second chamber to draw the portion of the meltedmaterial from the first chamber into the second chamber.